Method and apparatus for injection compression molding and ejecting paired thermoplastic spectacle lens suited for fully automated dip hardcoating

ABSTRACT

Plastic injection-compression multi-cavity molding of flash-free improved-cleanliness thermoplastic spectacle lenses (16) are suitable to be robotically dip hardcoated. Special spring-loaded (25, 26) molds having variable-volume mold cavities are used in an injection-compression molding process to form, without parting line flash, pairs of a wide range of differing optical power of polycarbonate Rx spectacle lenses (16). These pairs have special molded-on design features which are specially suited for full automation, starting with a novel way for ejection out of the mold into a takeout robot which is integrated via full automation with subsequent dip hardcoating. A molded-on tab with each pair of lenses is specially suited for manipulation by SCARA type robot. This combination produces micro-clean hardcoated paired molded lens made entirely within a single continuous cleanroom air enclosure surrounding the lenses, without any human operators therein, nor requiring any cutting or trimming of the molded paired lens or runner system before hardcoating, nor use of Freon (tm) CFC nor aqueous cleaning protocols before dipcoating.

This application is a divisional of application Ser. No. 08/533,126,filed Sep. 25, 1995, now U.S. Pat. No. 5,718,849.

FIELD OF THE INVENTION

The field of the present invention is plastic injection-compressionmolding of pairs of flash-free improved-cleanliness thermoplasticspectacle lens, to be fed into subsequent in-line dip hardcoating. Morespecifically, a method and apparatus for multi-cavity injection moldingof polycarbonate spectacle lens is integrated via full automation withdip hardcoating, to produce clean hardcoated molded lens made entirelywithin a single continuous cleanroom air enclosure surrounding thelenses, without any human operators therein, nor requiring any cuttingor trimming of the molded paired lens or runner system beforehardcoating, nor use of Freon (tm) CFC nor aqueous cleaning protocolsbefore dipcoating. An extension of this cleanroom enclosure and robotichandling may optionally provide in-line continuous-product-flowautomatic inspection of optical power and lens cosmetic quality, and/ormay optionally provide in-line continuous-product-flow anti-reflectivethin film vacuum coating, before the molded-and-hardcoated polycarbonatelenses exit out of the continuous cleanroom air enclosure and/or receivemanual handling.

BACKGROUND OF THE INVENTION A. Rx Lens Market Trend to Polycarbonate

The relevant product field is vision-corrective plastic ophthalmicprescription spectacle lens (hereinafter abbreviated "Rx lens") havingrefractive index greater than 1.530 glass and 1.49-1.50 "CR-39"(chemically, peroxide-crosslinked allyl diglycol carbonatethermoset-cast lens). This is the fastest growing category of Rx lensmaterials in the last five years, both in U.S. and worldwide markets.Such cast thermoset and injection-molded thermoplastics are so highlydesirable because the consumer/wearer of spectacle lens finds them to bethinner (due to greater light-bending power of high-refractive-indexplastic) and lighter (lower specific gravity, particularly in the caseof polycarbonate versus CR-39). As a result, the myopic ("near-sighted")spectacle lens wearer can avoid the cosmetically undesirable appearanceof "wearing coke-bottle glasses". In addition, lighter weight meansbetter comfort, less weight, less pinching at the nose and top of ears,where the loadbearing surfaces are.

Within this "thin & light", higher-refractive-index plastic Rx lenssegment, U.S. market statistics show a combined share of 25-30% of thetotal market. However, within this segment, the thermoset casthigh-index share has been essentially unchanged since 1991; nearly allthis growth in recent years is of the thermoplastic injection-molded Rxlens type, most specifically embodied by polycarbonate (R.I.=1.586).(Although there are other candidate high-index thermoplastics also beingconsidered, so far polycarbonate is most firmly establishedcommercially--hereinafter, "polycarbonate" will be taken to be inclusiveof other optical-grade thermoplastic substitutes, as would be obvious tothose skilled in the art).

The major reason for market share shift toward polycarbonate Rx lens andaway from cast thermoset high index Rx lens is reported to be theconsiderably lower manufacturing costs of polycarbonate Rx lens at highproduction volume levels. This, in turn, is from the high levels ofautomation attainable with polycarbonate, but inherently not attainablewith the more labor-intensive thermoset casting operations. Atlow-volume percent utilization, highly automated production can beburdened with extremely high fixed cost, but as volume increases past"breakeven" levels, there is a cross-over point where the relativelyhigher variable-cost inputs of labor and materials inherent to thermosetcasting becomes very disadvantageous. Thereafter, with increasingvolume, the incremental profit per unit of increased volume becomeshighly leveraged in favor of the more automated (polycarbonate)manufacturing operation.

This is reflected in market pricing from the lens manufacturers, whereinthe cast high-index hardcoated Rx lenses are far from beingprice-competitive with corresponding prescriptions of the multi-cavityinjection-molded, hardcoated polycarbonate Rx lenses (especially,finished single vision ("FSV") types which have higher unit salesvolumes per Rx). The cast high-index FSV can be typically 50-100% higherpriced. It is for these reasons why a further level of manufacturingcost reduction, through even greater level of automation and throughimproved capital efficiency (=lower breakeven volume, which reducescapital requirements for new manufacturing entries into the field) willbe strategically crucial in the polycarbonate Rx lens' future growth.

B. Prior Art Patents on Multi-Cavity Lens Molding and Dip Hardcoating

Today, polycarbonate Rx lens worldwide production is dominated by fourcompanies, together comprising an estimated greater-than-90% share ofworld market (although there are new entries just starting up). Each ofthese four currently employ some form of injection-compressionmulti-cavity molding process and apparatus, at the start of their "batchprocess" manufacturing flowsheet (see FIG. 4A Comparative Example). Thenext step is post-molding cutting of runner system and/or degating ortrimming off ejector tabs, so the trimmed lenses can be mounted into alensholder rack. Typically, these are semi-automatic operations assistedby a human operator, but they can also be entirely manual operations. Anexample of a molded-on hanger tab which is fitted to engage a Lensholderrack holding a plurality of such lenses is shown in Weber (U.S. Pat. No.4,443,159). The next step in the manufacturing flowsheet is to use someform of cleaning protocol (earlier versions were all Freon (tm) CFCultrasonic vapor degreaser methodologies; more recently, water-basedcleaning is aqueous high-pressure sprays with centrifugal spinning, ormulti-stage ultrasonic tank immersions, followed by drying operations).These cleaned and dried lenses are then dipcoated in liquid hardcoatingsolutions (either heat-curing silicone types or UV-curing types), andthe coating is cured by chemical crosslinking.

Two of the above-mentioned four polycarbonate Rx lens manufacturers arelicensees of Applicants' U.S. Pat. No. 4,828,769 and U.S. 4,900,242. Athird is Gentex Corporation, assignee of Weymouth (U.S. Pat. No.4,933,119). A fourth is Neolens, assignee of Bakalar (U.S. Pat. No.4,664,854). These patents employ some form of injection-compressionmolding process sequence with a plurality of mold cavities and employingvarious means for achieving cavity-to-cavity balance therebetween. Thesethree patents employed by four manufacturers differ in how the moldedlens is ejected out of the lens mold, as can be easily seen by observingthe O.D.-perimeter lens edge & sidewall of a sample lens from eachmanufacturer. More on this later in FIG. 2 and its descriptive text. Allthree necessarily do at least some cutting before dipcoating ispossible.

Looking at other prior art patents showing multicavityinjection-compression molding of Rx lens, Weber (U.S. Pat. No.4,008,031) apparatus for injection-compression molding of Rx lens showswhat appears to be a two-cavity mold. At 180 degrees opposite the gateinlet 23 is a hanger 20 for use in subsequent dipcoating operations.Weber also shows two molded-on ejector tabs 16, located at about10:30-1:00 o'clock positions, with respect to the gate/dripmark locationat 6:00 o'clock. Normally, this location would have the detrimentaleffect of propagating coating flowout runs along the front and backfaces of the molded lens during dipcoating withdrawal, but in Weber'scase, he has installed the hanger tab and ejector tabs onto acircumferential flange 12, which is set back from both the front andback lens edges, such that coating flow runoff could then follow thisflange from top to bottom of each individually-held lens (provided thelens don't swing from side to side).

Uehara et al (U.S. Pat. No. 5,093,049) also teaches and showsinjection-compression molding of Rx lens in a two-cavity mold, with thecavities connected by a cold runner and sprue, with the sprue being ableto be mechanically shut off at a predetermined time in the cycle, toprevent backflow. Uehara is silent on any ejection means for demoldingthese two lenses and no ejector tabs or pins are shown. If the forwardtravel of the movable cores, which provide the compression, is limitedby hard stops, they cannot be used to drive forward past the partingline once the mold is open, to assist ejection. In that case, a humanoperator would be relied upon to manually grasp the cold sprue and pullloose the two lenses attached thereto from the mold. No hanger tab isshown or mentioned.

Other historically important injection-compression molding of Rx lensesincludes Spector et al (U.S. Pat. No. 4,836,960) and Laliberte (U.S.Pat. No. 4,364,878), but both of these are limited to single-cavityembodiments.

Looking now at Rx lens dipcoating prior art patents (in additioon topreviously-cited Weber (U.S. Pat. No. 4,443,159), Laliberte (U.S. Pat.No. 3,956,540 Method and U.S. Pat. No. 4,036,168 Apparatus) teaches aform of conveyorized transfer of such lensholder racks through amulti-station machine internally having a filtered-air cleanroomenvironment, wherein the lenses are successively ultrasonically cleanedand destatisized, then dipcoated, then dried and at least partiallycured to a tackfree state before the conveyor takes them to aloading/unloading station, where the lenses can be removed by theoperator. Similar configurations were developed using differentautomated transfer means, including two chain-drive conveyors operatingin parallel and connected by crossbars whereon the lensholder rackswould be hung, or, alternatively, an overhead conveyor with power andfree flights for indexing could be used, with suspended removablelensholder racks mounted thereon. Such configurations for polycarbonateRx lenses (and non-Rx lenses) typically used at least one (preferably,two, in series dips) Freon ultrasonic cleaner/degreasers, wherein thepolycarbonate lenses were immersed in the ultrasonic sump for aprescribed time, during which cavitation (generation and collapse ofmicroscopic bubbles) provides high kinetic energy workingsynergistically with the Freon's solvency (to reduce adherent filmsholding onto the soils on the lens surface), to thus dislodge and floataway surface contaminants of both soluable and insoluable types. Afterlens removal from the ultrasonic sump solution, an azeotropicfreon/alcohol vapor zone would help rinse and dry the lens before goinginto the dipcoating tank.

Liebler et al, UK Patent Application GB2 159 441 A, published 4 Dec.,1985; assignee: Rohm GmbH) also teaches continuous dip production ofscratch-resistant liquid coatings onto plastic optical moldings (such aslenses). It specifically teaches an endless conveyor belt to transferlensholder racks containing a plurality of lenses. Among the opticalplastic moldings contemplated are spectacle lenses, and FIG. 2 shows amolding with a "lug 10 for clamping purposes is formed thereon anddiametrically opposite this lugged end is a dripoff lug 11, so thatexcessive scratch-resistant coating composition can drip off withoutforming a ridge when coated and dried." (Lines 97-105). In comparison toLaliberte, this machine is far simpler, contemplating merely aload/unload, a liquid dipcoating station, and a drying station shown(described as, "preferably, two or more infrared radiators". Not shownbut mentioned in text is . . . "cleansing bath may also be providedupstream of the inversion bath. The cleansing bath may, for example, bean ultrasonic bath containing organic solvent". (Lines 122-128).However, Liebler is believed not to have ever been actually used forspectacle lens coating nor Rx lens coating. There are major technicalproblems unforeseen by Liebler. His FIG. 2 lens withdiametrically-opposed hanger tab and drip tab would inevitably havecoating flowout runs propagated from the two junctions of the coatingtab, at its shoulders. Unfortunately, these runs take place in the veryworst location of the perimeter, since the coating flow runs will godirectly through the central, most critical zone of the optics forvision (see Comparative Example FIG. 2D). To the extent that the Lieblerapparatus might be acceptable, it would not be believed to be spectaclelenses, but rather ordinary protective-covering lenses such as watchglasses, scales, and mirrors, none of which are required to have thehigh quality of image transmission that corrective-vision spectaclelenses must have. Where the hardcoating merely is to protect from heavyscratching and the protective-covering lens is merely to provide sometransparency to a product or device, such flow runs may be harmless andnot a functional problem. However, for spectacle lenses with humanvision problems resulting from optical aberrations, such coating flowruns would be completely unacceptable and the source of very highpercent rejectable flaws. If such tab configurations are as shown, ofthe full thickness of the lens molding, then such a problem would beabsolutely intrinsic. However, if the tab is not of the full thicknessof the lens, as shown in the Weber drawings, but merely thick enough tosupport the relatively light weight of the lens suspended thereby, thensuch a tab location would be acceptable, but only if the lens is heldlevel in its mount, not rocking back and forth, which would be a anotherproblem envisioned with Liebler's "endless conveyor".

C. Environmental and Economic Problems with Lens Cleaning

"Freon" cleaning is based upon now-unacceptable CFC-113(ozone-depleting), production of which theoretically ceased on Dec.31st, 1994, in accordance with the Montreal protocol and its EUrevisions. As a result, new Rx lens installations necessarily havesubstituted aqueous cleaning approaches instead. One such approachemploys high-pressure (up to 20,000 psi) jets of water spray which arescanned across the front and back surfaces of the lens, by moving thelens (such as spinning it on a spindle) or by moving the spray head(such as by reciprocating motion) or preferably, a combination of both.High-pressure water spray is very effective in removing insolubleparticulate forms of surface contamination (such aselectrostatically-held polycarbonate dust particles or airborneinorganic dusts) but has the drawback that such cleaning is 100% "lineof sight", so not only must lenses typically be cleaned one at a time,but a typical spin/spray combination requires one side to be cleaned,then manually or robotically flipped over and placed back on a differentspindle to clean the second side. The throughput of such equipment(number of lenses per hour) versus the labor cost and capital cost isvery much higher than the old Freon cleaners it replaced, which are nowenvironmentally unacceptable.

A second way of aqueous cleaning is to have an ultrasonic, water-baseddetergent solution in the first stage of a countercurrent-flow,multi-station, automated cleaning line with conveyorized transporttaking the lenses through successive immersion tanks (typically, atleast five, and preferably 7-15 stations, including deionized waterrinses).

Whether by high-pressure water spray or by ultrasonic, multi-stage tankimmersions, the resulting clean-but-still-wet polycarbonate lens cannotyet be dipped into the liquid hardcoatings (which are all chemicallyincompatible with any significant % water), so they still face anotherproblem, and that is how to completely remove all the remaining waterfrom the lens (and/or its lensholder rack), without creating superficialstains ("water spots") on the lens' optical surfaces. In the case ofwater-immersion tanks, the last tank is typically maintained at a veryhigh temperature, near the boiling point of water (which can cause lens"fogging" due to high % humidity inside the cleanroom wherein dipcoatingdrydown must also be done), and the withdrawal rate of the lenses beingremoved from the tank is extremely slow, to encourage capillary effectto maximize water removal. In the case of spin/high-pressure spray,centrifugal action of high-RPM spinning speeds is attempted to sling offall excess water. Nevertheless, because the liquid hardcoating solutionscannot stand even small amounts of water "dragout" introduced by lenses(even small droplets of water will result in streaky or spotty foggingof the coated lenses or blotchy appearance). So, inevitably, ahot-air-circulating dryer (filtered for cleanliness) must be used, whichmakes for an energy-intensive and costly operation. The multi-stationautomatic-transfer water cleaner in-line system takes up a great deal offloor space and costly (multi-$100,000). In addition, disposal of theliquid effluent from these aqueous cleaning solutions is turning out tobe an environmental problem not previously encountered with the Freoncleaners it replaced.

OBJECTIVES OF THE INVENTION

For these reasons, one objective of the present invention is to producecleanly-demolded multicavity Rx lenses which are ready to dipcoatwithout cutting or trimming, nor any use of Freon or aqueous cleaningprotocols, with a molded-on harder tab having special design suited forrobotic handling and transfers.

Another objective of the present invention is to have no human operatortouch the lenses, starting from the time that multicavity demoldingstarts until after the hardcoating is at least partially cured to atackfree state. Preferably, for minimal airborne contamination, no humanoperator will even be inside the same cleanroom airspace which surroundsthe lens from start of demolding until after the hardcoating is at leastpartially cured to a tackfree state.

Another objective of the present invention is to increase productivityby changing the "unit of transfer" being handled from individual Rx lensof the prior art to paired molded-together Rx lens, which come from themold ready to be robotically handled by means of the molded-on hangertab having special design.

Another objective of the present invention is to minimize any plastic"flash" at the parting line edges of the paired molded lenses, so as toprevent dipcoating flow runs propagated off such flash and/or toeliminate any trimming off of flash before dipcoating, since suchtrimming processes generate plastic airborne particulate contaminations.

Another objective of the present invention is to be able to demold thelens cleanly, with ejection processes generating minimal (or none) metalor plastic airborne particulate contaminations.

Another objective of the present invention is to further reducemanufacturing costs of Rx polycarbonate lenses by improved % yields,less work-in-process inventories, and better labor productivity by thisnovel fully-automated continuous-process flowsheet vs. prior artbatch-process flowsheet.

SUMMARY OF THE INVENTION

The present invention employs "design for manufacturability" principlesfound lacking in the prior art. An essential element of the presentinvention is that the unit of transfer, from the demolding step onthrough the coating-and-curing step, should be a pair of Rx lenses, notindividual Rx lenses. Thus, each time a robotic transfer takes place,output is effectively doubled in this way. This insight is not found inthe prior art, which teaches and shows only one single lenses per tab.

A second element is to provide means for a flash-freeinjection-compression molding process, using 2-stage spring-loadedforces which determine the cavity height of variable volume moldcavities during the filling and the ejecting phases of the cycle. (Asused herein, "parting line flash" means plastic spilled out of themoldset along the parting line where the A side and B side of themoldset joins). Since any plastic "flash" at the parting line edges ofthe paired molded lenses is most likely to occur in the last fractionsof a millimeter of the "mold-closing" compression stroke during such afilling process, this element greatly increases the spring forces whichhold the moldset's parting line shut only during this lasthalf-millimeter of compression stroke. Eliminating flash preventsdipcoating flow runs which readily propagate off such flash and/or toeliminate any trimming off of flash before dipcoating, since suchtrimming processes will generate plastic airborne particulatecontaminations.

A third element is novel demolding operations which minimize oreliminate generation of airborne particulates which can contaminate themolded Rx lens product. This element first is embodied into Rx lensproduct design, most specifically, the lens edge detail geometry.Secondly, apparatus considerations must be built into the mold design toprovide the required process steps of automatically stripping moldedpaired Rx lens off, when the mold is fully open and a robot arm withsuitable gripper jaws is in its proper location to receive the ejectedpaired molded Rx lens (no manual assistance is to be needed duringdemolding.)

A fourth element of the present invention is elimination of all cuttingor trimming of solidified thermoplastic once demolding has occurred,until after dipcoating has been applied and cured at least to a tackfreestate. Eliminating flash by improved molding process (by the 2-stagespring force) is better than trimming flash off later. Any ejector tabsor drip tabs must be suitably located along the lens perimeter so as notto interfere with proper dipcoating and not to propagate coating flowoutruns. Specifically, no such tabs will be placed in the upper 90-degreequadrant (defined as 10:30-1:30 o'clock locations) of the lensperimeter. The molded paired Rx lens must be connected therebetween by acold runner, with said runner located in the 1:30-4:30 o'clock sidequadrant for the left lens and the 7:30-10:30 o'clock side quadrant forthe right lens.

A fifth element of the present invention is an integrally-molded hangertab, typically located substantially equidistant between the two lensesin the molded pair and rising substantially vertically off of thecold-runner connecting the paired lens (such symmetry has the advantageof minimizing side-to-side tilting of the paired lens). In an optionalbut preferred embodiment, the head of this molded-on hanger tab will beabove the highest top edge of the molded pair when held vertically, soas to prevent the liquid dip hardcoating from contacting the roboticmeans for gripping the head, so the stem length between the head and thecold runner should be at least sufficiently above said top edge of lens.Most preferably, the stem will be sufficiently longer so that a secondgripping position with protruding slide-stop can be located also abovethe top edge of the paired lens. (In an alternative optional butless-preferred embodiment, the head of this molded-on hanger tab will bebelow the highest top edge of the molded pair when held vertically, usedwith periodical clean-off of the accumulated dip hardcoating which hascontacted and cured onto the robotic means for gripping the head.)Special features are designed into the head so as to geometrically matewith certain robotic devices, workholders and racks.

Optionally, a drip tab is located in the bottom quadrant of each lens(4:30-7:30 o'clock positions), to minimize dipcoating dripmark size, bycapillary wicking action to drain off excess liquid coating once themolded paired lens have been fully removed from immersion in thedipbath. These optional drip tabs would, however, have the disadvantageof requiring a trimming operation after coating is cured, and also theywill increase polycarbonate resin usage+cost per lens.

These four elements of the present invention enable multi-cavityinjection molding of polycarbonate spectacle lens to be integrated viafull automation with dip hardcoating, to produce clean hardcoated moldedpaired lens made entirely within a single continuous cleanroom airenclosure surrounding the lenses, without any human operators therein,nor requiring any cutting or trimming of the molded lens or runnersystem before hardcoating, nor use of Freon CFC nor aqueous cleaningprotocols before dipcoating. The novel combination of Applicants'lensmold processes and apparatus and molded lens design for themanufacturing processes contribute to this end. An extension of thiscleanroom enclosure and robotic handling may optionally provide in-linecontinuous-product-flow automatic inspection of optical power and lenscosmetic quality, and/or nay optionally provide in-linecontinuous-product-flow anti-reflective thin-film vacuum coating, beforethe molded-and-hardcoated polycarbonate lenses exit out of thecontinuous cleanroom air enclosure and/or receive manual handling.

Another novel improvement using a special spring-loaded assembly of 2different types of springs has been shown to reduce parting line flashin variable volume injection-compression molding process, applicable toany edge-gated molded plastic article.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 1A and 1B show a two-cavity Rx lens mold of the presentinvention, in 2 cross-sectional split views (showing different stages ofmolded lens formation and ejection/demolding steps within a singlemolding cycle) and in a plan view.

FIGS. 2, 2A, 2C and 2D show comparative examples from selected priorart, with special attention paid to location of dripmark and ejectortabs or gates that need to be cut before dipcoating can take place, aswell as orientation of hanger tabs.

FIGS. 3 and 3A-3D show the paired molded lenses after ejection, withpreferred hanger tab location and stem length, and specific head andstem configurations of the present invention suited for mating withdifferent variations of robotic gripping position and workholder matinggeometries.

FIGS. 4A-4D show manufacturing flowsheets, with the process steps shownin block diagram and those steps which are to be done robotically withina cleanroom are shown within dashed-line boxes.

DETAILED DESCRIPTION OF THE INVENTION A. Lens Formation and Ejectionwithin Moldset.

The present invention employs a novel and advantageous method andapparatus for ejecting multi-cavity injection-compression-molded Rxlens, in molded pairs each with a hanger tab (see FIG. 3), whilepreserving cleanliness of both the demolded paired lenses and theoptically polished molding surfaces of moldset, free of metal or plasticparticles. Refer to FIGS. 1, 1A and 1B, showing a simplified two-cavitylens moldset, with the injection molding machine nozzle tip (not shown)injecting into a cold sprue bushing (9) and cold runner system (15)which is centered between the two mold cavities. An optional butpreferred embodiment for molding two or more pairs of Rx lenses duringone cycle of a single moldset would employ instead a hot-runner systemusing a plurality of hot-runner nozzle tips in place of the singleinjection molding machine nozzle tip which injects into cold spruebushing (9) and cold runner system (15); such a hot-runner apparatus fora four-cavity mold is shown in Applicants' U.S. Pat. Nos. 4,828,769 and4,900,242 (incorporated herein by reference), FIG. 17. Anotheralternative hot-runner system for optical thermoplastic molding is shownin Applicants' U.S. Pat. No. 4,965,028, incorporated herein byreference. A cold well (40) is advantageous to build into the cold sprueand cold runner system, to trap "cold slugs" before they reach the lensmold cavities. Note that a slight undercut (41) or negative draft angleon cold well (40) will provide a positive mechanical retention force,which is helpful later on in ejection steps.

Another optional but preferred embodiment for molding pairs of Rx lenseswithin a single moldset would employ "variable volume" mold cavities,wherein the initial cavity height dimension is larger before injectionstarts than the final molded lens thickness dimension. Such a "variablevolume" mold cavity moldset apparatus typically uses aninjection-compression molding process sequence to mold the Rx lenswherein a driving force squeezes the injected melt sometime afterinjection starts to reduce this cavity height dimension (refer to citedprior art lens molding patents for various schemes for driving forcesand sequences). A preferred one shown in Applicants' U.S. Pat. Nos.4,828,769 & 4,900,242 employs a resilient member 13 (such as a hydrauliccylinder or a mechanical spring) of FIG. 10B to determine the cavityheight dimension, so that when the resilient member 13 is extended oruncompressed, the cavity height dimension is larger, by a compressionstrokelength 40 dimension, and when the resilient member 13 iscontracted or compressed (such as by increased mold clamping forcesexerted by the injection molding machine squeezing the platens together,most preferably before injection is completed), the cavity heightdimension is made smaller by making the compression strokelength 40dimension become zero. See FIGS. 2-8 which show this injectioncompression process sequence throughout one complete molding cycle.

It has been found by Applicants since that patent was filed that use ofhydraulic cylinders for the resilient member 13 within polycarbonate Rxlens molds is disadvantageous, since such moldsets run at very hot(240-295° F.; 120°-150° C.) temperatures, causing seals to leak and oilto contaminate the partforming surfaces. Use of conventional coil-typedie springs as resilient member do not have that problem, and arelong-lived, and can give the long compression strokelenths (as high as0.400" or 10 mm has been used to mold very high minus power Rx lens with1.0-1.5 mm lens center thickness with 10-14 mm edge thicknesses withminimal "knitline"). However, they have flash problems duringmoldfilling; to eliminate parting line "flash", the spring force holdingthe parting line shut must exceed the force of melt pressure beingexerted upon the projected area wetted by melt, and within the last0.1-0.5 mm of the compression stroke is when typically such flashing canoccur. Parting line "flash" (plastic spilled out of the moldset alongthe parting line where the A side and B side of the moldset joins) mustalso be eliminated or minimized, as it will otherwise be trimmed offbefore dipcoating (thus generating particulates) or it may create liquiddipcoat flow runs. Use of extremely stiff, high-deflection-forceconventional coil-tape die springs as resilient member to solve thatproblem create a different problem during the ejection phase of themolding cycle, however, since as soon as the clamping force is releasedin preparation for mold opening, these high spring forces act as acatapult for the lenses and cold runner by prematurely pushing forwardthe parting line molding surfaces before the injection molding machine'sejection mechanism is actuated.

The present invention preferably can employ a novel combination of 2different types of moldsprings within the moldset to give "2 stage"workings of these "resilient members". As shown in FIG. 1, (shown insplit cross-sectional view, when the spring is uncompressed, such as byreleasing mold clamping forces exerted by the injection molding machineduring ejection phase of the cycle), a conventional coil-type steel diespring (25) having long compression strokelengths but moderatedeflection force are used in combination with extremely stiff, very highdeflection force stack of Belleville spring washers (26) held in placeby shoulder bolt (29), to give 2 different levels of moldspring forcesduring 2 different phases of the strokelenght--when either initialmold-opening or final-closing movements are in the 0.0 to 0.5 mm range,the very high deflection force stack of Belleville spring washers (26)dominate; from then on, the weaker coil-type die spring (25) are theonly applicable spring force, giving a controllable mold-opening-stroke(too high spring forces can then almost "catapult" the paired moldedlenses off the B side, held on only by retention (41)). Together, theydetermine the variable volume cavity height dimension, on each moldingcycle to create a compression strokelength (21), up to a maximumdimension determined by shoulder bolt (29) In such an optional butpreferred embodiment of the present invention, this injectioncompression process sequence is as shown in Applicants' U.S. Pat. Nos.4,828,769 & 4,900,242 FIG. 2-6, but differ thereafter (not as shown inFIG. 7 & 8), in how the Rx lenses are to be de-molded and ejected. For aflash-free injection-compression mold filling process, using 2-stagespring-loaded forces greatly increases the spring forces which hold themoldset's parting line shut, only during this last half-millimeter ofcompression stroke. This process automatically changes the sum of the 2springs' force just when greater force is needed, in the last factionsof a millimeter of the "mold-closing" compression stroke during such avariable volume mold filling process.

Applicants' 2-stage springload combination (stiff-spring applied only ashortstroke+soft-spring applied over the whole longer stroke) is animproved form of "resilient member" operating within any suchvariable-volume injection compression mold in which the cavity height isdetermined by the degree of elongation of springs. A review of the priorart cited herein and cited in Applicants' U.S. Pat. Nos. 4,828,769 &4,900,242 shows no such 2-stage springload combination, nor any suchinsight into the benefit thereby. Specifically, any edge-grated plasticarticles to be molded within a variable-volume injection compressionmold in which the cavity height is determined by the degree ofelongation of springs will have the same tendency toward parting lineflash, and the larger the projected area of the cold runner system(especially if large fan gates or full-length runner-gating is used),the worse the flash problem will be. If the article is flat and meltflowpathlength is short, then a very short (0 to 1 mm) compressionstokelength can be used, for which a single very stiff spring geometryis satisfactory, so Applicants' novel 2-stage springload combination isthen unnecessary. However, if the article is of non-flat contour andmeltflow pathlength is longer, then a longer (>1 mm; typically 2-10 mm)compression strokelength must be used, for which a single very stiffspring geometry is unsatisfactory, Applicants' novel 2-stage springloadcombination is then useful and necessary, to control flashing tendency.Such other articles may be other precision optical lens products (suchas light-amplifying LCD lens arrays for flat panel displays, manyoptically microstructured surfaces replicated through molding including"binary optics", "hybrid optics", fresnels and holographic imaging) andmolded automotive windows, headlamp lenses, and mirrors, but flashfreenon-optical opaque injection-compression moldings of similar geometriesis also contemplated, such as large auto exterior body panels (hoods,doors and fenders) and in-mold-textile-surfaced interior panels. Allthese non-spectacle-lens applications are known to have considered orused variable-volume injection compression molding, and the flashproblem is believed to have detered some from actual use. Applicantshave recently run such variable-volume injection compression molds withand without the novel 2-stage springload combination, and these testshave proven clearly the anti-flash benefits claimed.

Such an injection-compression molding process for reduced parting lineflash on at least one molded thermoplastic article operates within amoldset mounted within an injection molding machine having programmablecontrol of means for applying clamping forces and opening forces onto aparting line formed between A side and B side of the moldset, and theinjection molding machine has programmable control of means for movingforward or hack an ejector assembly within the B side of said moldset.The moldset has at least one edge-gated variable-volume mold cavityhaving partforming surfaces on opposing paired A side insert and B sideinsert facing the parting line, and at least one extendable andcompressible passive resilient member of varying length determines acavity height dimension of the mold cavity within preset mechanicallimits. The resilient member being an operative combination of:

i) steel coil die spring to provide a moderate spring force over a verylong distance in a first clamping position of the moldset, with

ii) stacked Belleville type steel spring washers to provide a very stiffspring force over a very short distance in a second clamping position ofsaid moldset, with the resilient member being mounted between the B sideparting line mold plate and B side clamp plate of said moldset, andexerting combined spring forces to bias forward the B side parting linemold plate toward the parting line. In the injection compression moldingprocess,

when there is less clamping force exerted by the injection moldingmachine than a first spring force equal to the steel coil die springforce acting alone to bias forward the B side parting line mold platetoward the parting line, the resilient member length will be a maximumwithin the preset mechanical limits in a first clasping position of themoldset, and

when there is more clamping force than the first spring force equal tothe steel coil die spring force acting alone to bias forward toward theparting line but less clamping force than a second spring force equal tothe steel coil die spring acting together with steel spring washer forceto bias forward the B side parting line mold plate toward the partingline, the resilient member length will be an intermediate value in asecond clamping position of the moldset, and

when there is more clamping force than the second spring force equal tothe steel coil die spring acting together with steel spring washer forceto bias forward the B side parting line mold plate toward the partingline, the resilient member length will be a minimum within the presetmechanical limits in a third clamping position of the moldset.

This process has the steps of:

a.) Pre-enlarging the mold cavity by substantially closing a perimeterof the mold cavity at the parting line so as to prevent moltenthermoplastic from flushing, in a first position of the moldset formedby applying a clamp force equal to a first spring force, such that afirst cavity height equal to the sum of the desired compressionstrokelength plus a final thickness of the molded article is determined,before injection starts;

b.) Partially filling the mold cavity after injection has started byprogressively reducing cavity height in a second position of the moldsetformed by increasing clamp force applied to exceed the first springforce but less than the second spring force;

c.) Completely filling said mold cavity after injection has ended byfurther progressively reducing cavity height to reach a third positionof the moldset formed by increasing clamp force applied to exceed thethe second spring force;

d.) Cooling said molded article within the mold cavity after injectionhas ended by maintaining cavity height substantially at the thirdposition of the moldset formed by maintaining clamp force applied toexceed the the second spring force until a maximum cross section isbelow a glass-transition temperature characteristic of thethermoplastic;

e.) Ejecting the molded article by releasing clamp force and opening themoldset along the parting line.

In accordance with the present invention, once the optical-gradethermoplastic has cooled to at least the glass-transition temperature(for polycarbonate, this equals 296° F.) in even the thickest crosssection, then the resulting molded lens should be shape-stable (theplastic molecules will have memory). Since molding productivity isenhanced by faster heat transfer rates between the cooling melt and themold inserts, it may be advantageous to employ highly-conductivecopper-based alloys, with a hard electroplated chrome or nickel face onthe optically-polished partforming surfaces, as materials forconstruction of the mold inserts. Applicants' U.S. Pat. No. 4,793,953(incorporated herein by reference) is one such example, for use inoptical molding. A further improvement in optical molding thermodynamicsis Applicants' U.S. Pat. No. 5,376,317 (incorporated herein byreference) employs such highly-conductive copper-based alloy moldinserts in a molding cycle which starts with mold insert surfacetemperatures above the glass-transition temperature, then after the moldcavity is filled and packed, drops the mold temperature far below thenormal hot (240-295° F.:120-150° C.) temperatures used for Rxpolycarbonate lens molding.

The first step of demolding and ejection of the paired lens starts withreleasing clamping forces applied by the injection molding machine,thereby decompressing and extending the resilient member comprising thecombined springs described above. See FIG. 1B, righthand split view,showing the molded lens (16) as already been separated off the B sidecore insert (14) optically-polished partforming surface, creating arelease space (17) between the concave lens surface and the convexinsert surface upon which it was formed. This release space (17)substantially corresponds to the compression strokelength (21)dimension, when the moldset spring is extended or uncompressed byreleasing mold clamping forces exerted by the injection molding machineduring the very start of the ejection phase of the cycle. At the sametime, drafted sleeve surface (19) forming the lens edge uses thermalshrinkage of the molded lens to assist separation off the mold cavitybore (sleeve 20) surfaces. Importantly, were zero draft employed in thebore which forms the lens edge, as is common in today's Rx polycarbonatelenses made by prior art methods, these lenses could be so strongly heldonto the B side mold insert (14) by partial vacuum that the lenses arepulled back when the springloaded parting line B side mold plate (28)comes forward (relative to the B side mold insert). Applicants have seensuch examples, where the still-hot gates are bent or, even worse, tornoff, leaving the lens stuck onto the B side insert deep inside the bore.By applying some positive draft to the B side sleeve, a mechanicalinterference is created which prevents this possibility of the lensesbeing pulled back into the bore.

See FIG. 1B. Note that the parting line (C--C cross-sectional plane) isnot yet opened at all, even though the movable platen has traveledrearward (compare the moldset height measured between A clamp plate (25)and B clamp plate (23) vs. the lefthand split view which shows thefully-clamped condition). With or without an optional air blowoff, whenthe parting line starts to open up, the molded paired lenses are alreadytransferred off the B side and are being pulled off theoptically-polished partforming surfaces of the A side concave inserts(13). since the cold sprue (18) and cold runner (15) of the moldedpaired lenses are still firmly attached to the ejector mechanism (whichis not yet actuated), using conventional mechanical retention (41)(shown as controlled-draft-angle on the cold well (40) of the sprue) to"grip" the molded paired lenses (16) onto the B side. (Also,deliberately running the coolant temperatures on the B side cooler thanthose of the A side can cause more shrinkage to occur on the B side ofthe molded lenses, thus reducing retention forces on the A side of thelens.)

See FIG. 1. As the injection molding machine's mold opening continuesafter the maximum forward travel of the springloaded B side mold plate(28) is reached (set by the shoulder bolt (29)), then the parting lineopens up. Once the A & B sides are no longer held together, strippingforces are automatically applied by this mold opening motion which willexceed the partial vacuum that may exist between the convex surface ofthe molded lens and the corresponding concave mold insert surface uponwhich it was formed, since the molded paired lens are still held bymechanical retention forces (41) onto the movable platen B side of themoldset. As long as these B side retention forces exceed the forcewanting to hold the lenses onto the A side inserts without exceeding thecohesive strength of the plastic in the cold runner and gate, pullingthe lenses off the A side will be mechanically positive when the partingline opens up sufficiently during mold opening.

Next, as shown in FIG. 1, the paired molded lenses (16) and connectingcold runner system including mechanical retention (41) are stripped offthe B side by conventional ejector pins (4), which are driven by motionsof the injection-molding machine's hydraulic ejector cylinder (notshown) tied into the moldset ejector plates (24), to which the ejectorpins (4) are mechanically tied in. Stripping the lenses off the B sidewill also be mechanically positive. This step is done only when themoldset is fully opened up along the parting line, and timing of thisejector motion is only initiated after the end-of-arm tooling of atakeout robot is in place to receive the molded paired lenses whilebeing stripped off of the mechanical retention. This timing iscoordinated between a programmable control of the injection moldingmachine and of the takeout robot, with part verification to confirm thatthis handoff has been made. Many brands and types of takeout robotsexist for plastic injection molding machines. A side entry type ispreferred over the more common "up and out" rectilinear type, since thespace above the mold platens is preferably where downward-facing HEPAfilters will be located, and since a cleanroom enclosure will be smallerand more compact if a side entry type is used. Typical makers of sideentry takeout robots include Ranger Automation of Shrewsbury, Mass.,Conair Martin of Agawam. Mass., and Automated Assemblies of Clinton,Mass.

Note that the above-mentioned ejection sequence differs from theconventional way plastic parts are ejected from injection molding, whichstarts by stripping the molded part off the partforming cavity surfacefirst, when the mold starts to open, while holding the molded part ontothe partforming core surface. After the mold is fully open, either arobot arm or human operator then reaches in and pulls the molded partoff the partforming core surface.

In an optional but preferred embodiment of the present invention,filtered compressed air is employed in accordance with a prescribed "airblow" sequence of steps in order to provide a supplementary drivingforce for separating the molded lens off the optically polishedpart-forming surfaces, to which they are held by natural vacuum due tothermal shrinkage while the mold is closed and the clamping force ismaximized. Although use of compressed-air blowoff to assist ejection isnot new to those skilled in the art of injection-molded thermoplasticsgenerally, Applicants are not aware of it ever being employed in opticallens injection molding, and it is not found in any of the prior-artpatents relevant to this field. Refer to FIG. 1B. Applicants employfiltered compressed air (for cleanliness of part-forming mold surfacesas well as molded lens surfaces), introduced by A side air line (10) andB side air line (11), into the clearance gap (12) formed between theouter perimeter of each cavity insert (A side cavity insert (13) and Bside core insert (14)) and the bore of circumferentially-surroundingsleeve (20). Air valves (not shown) control the air flow and pressurewithin air lines (10) and (11) to provide air blow in an ejectionsequence, working in combination with conventional ejector pins (4),which are driven by motions of the injection-molding machine's hydraulicejector cylinder (not shown) tied into the moldset ejector plates (24),to which the ejector pins (4) are mechanically tied in.

In an optional but preferred embodiment of the present invention, evenbefore the parting line is opened, filtered compressed air feeds throughthese "vent gap"-sized passageways gap (12) (for polycarbonate lens, agap of 0.001"(0.025 mm) still will not "flash"), so that the forces ofthe air begin to be applied on the movable platen B side (core side)around the perimeter of the convex insert, and work inward toward thecenter of the lens, to provide a clean separation off the convexpart-forming surfaces of the B side insert. At the same time, draftedsurface (19) of the lens edge uses thermal shrinkage of the molded lensto assist separation off the mold cavity bore (sleeve 20) surface. Toassist separation of the paired lenses off the stationary platen (Aside) of the mold before the parting line is opened, in an optional butpreferred embodiment of the present invention, a second stage of airblowoff can be initiated, wherein similarly filtered air enters uparound the perimeter of the concave optically-polished A side moldinsert perimeter and driving toward each lens center to break thepartial vacuum formed during molding. During this time, a substantialseal is still held by a tiny edge seal overlap (42) of the lens frontonto the lens mold cavity perimeter. See FIG. 1B. If this tiny sealoverlap (42) is missing air blowoff forces will be substantiallyweakened and may be ineffective, since the air will follow the path ofleast resistance and bypass the lens center, leaving some partial vacuumforce wanting to hold the molded lens in place during the next stage ofejection, which is mechanical stripping the lens off the concave insertsurfaces by the molding machine's clamp-opening stroke while the pairedlenses are being firmly held onto the ejector apparatus which movesalong with the B side of the moldset.

B. For Cleanliness, Never Cut Solidified Plastic Before Dipcoating

Each polycarbonate (dipcoated lens is inherently edge-gated and ishardcoated by a glossy film which is easily seen to form a "dripmark"(resulting from gravity flow of the liquid dipcoating onto both frontand back surfaces). To examine such an Rx lens, let us look at a planview of the molded hardcoated lens, and find the location of thedripmark (easily observed as a buildup (37) of the relatively-thickerhardcoating glossy film, as seen in FIG. 2B. When laid out as a clockface, let us arbitrarily designate the location of any lens' dripmark asin the 6 o'clock position. By examining this lens-edge sidewall,starting at the dripmark and going circumferentially all the way around,one can see if any ejector tabs were used, and if so, were the cutbefore or after dipcoating, because if these tabs would be cut offbefore or dipcoating, it will show a glossy covering over the cutmark/residue, in addition to the degating residue where the gate hasbeen removed.

Observing lenses sampled from the current market, the Gentex and Neolenslens samples typically show one or more ejector tabs, most commonly 180degrees opposite the gate. The Neolens sample showed four such ejectortabs+the gate, all of which were cut off before the cleaning anddipcoating operations (like Comparative Example FIG. 2.)

The reason why tabs in some lens edge locations cannot be tolerated inthe dipcoating process is that liquid coating on the top half of thelens would run down by gravity from the tip of the ejector tab over thelens edge, and this liquid stream of coating will then flow verticallydown from that perimeter location of the ejector tab along the front orback optical surface of the lens. This "coating flow runs" createsnonuniform lightbending (=aberrated image seen when looking through theaccumulated thicker coating), causing a rejection of the manufacturedlens. If one or more ejector tabs must be cut off the moldedpolycarbonate lens before dipcoating, this not only adds to the variablecost (higher resin used per lens, more labor cost for operator handlingand trimming operations, but it also directly reduces surfacecleanliness of the freshly-molded lens. There is no way to cleanly cutsolidified polycarbonate plastic without inevitably generating fineairborne particulates ("polycarbonate dust"), which immediatelyre-deposits onto the front and back optical surfaces of thepolycarbonate lens, because electrostatic attraction forces will drawand bind them to the high-dielectric-constant polycarbonate surfacelayer. Use of ionizing-air blowers can minimize this electrostaticattractive force, but actual tests of freshly demolded lenses withfieldmeters show 5-30 kilovolts of static charge, which is only veryslowly dissipated (in minutes, not seconds) due to excellent electricalinsulation properties of polycarbonate.

Even then no ejector tabs are cut before coating, if the lens must bedegated so that it can be hung via molded-on hanger tab onto thelensholder rack (see Comparative Example FIG. 2), or if a molded pair ofthe lens must have the cold runner cut so that it can be inserted viamolded-on hanger tab into the lensholder rack (see Comparative ExampleFIG. 2A), then these degating and/or runner-cutting operations will alsogenerate the fine polycarbonate dust as airborne surface contaminants.All apparently also some require manual handling by human operatorbetween molding and dipcoating steps. After trimming and mounting intolensholder racks, these polycarbonate lenses are cleaned to remove anysoluble surface contaminants (such as oil) and insoluble particulatesoils (such as airborne inorganic dusts, but most troublesome, the finepolycarbonate particles generated by the trimming and degating andrunner-cutter operations).

Applicants' U.S. Pat. No. 4.828,769 and U.S. Pat. No. 4,900,242licensees' lenses do not use any ejector tabs, as can be verified byexamination of the lens edge. Nevertheless, if the injected shot (into aplurality of lenses connected by cold-runner melt delivery system) mustbe cut apart in order to be mounted into lensholder racks, then theserunner-cutting operations have the same undesirable effect of generatingpolycarbonate dust. The statistically greatest source of percent yieldloss is the flaw category known as "coating clear specks", wherein atransparent/translucent particle, of sufficient size and location so asto disturb vision is encapsulated inside the liquid-appliedhardcoating's glossy film. Obviously, vigorous cleaning and multi-stagedilution factor can make a difference in reducing this economic loss andpercent yield. Nevertheless, even with today's best cleaners, it remainsthe greatest source of scrap lenses.

Refer to FIG. 1A. The molded paired lenses of the present invention willhave no hanger tabs (1) in the upper 90-degree quadrant (6) (between10:30 and 1:30 o'clock), will be gated (4) within right and/or left sidequadrants (5) and (-5) (between 1:30 and 4:30 o'clock for (5) andbetween 7:30 and 10:30 o'clock for (-5). respectively), and if they usean (optional) drip tab (not shown), it will be located in lower quadrant(7) (between 4:30 o'clock and 7:30 o'clock). See also hanger tab stem(3) and open-spring head configurations described more in examplesreferring to FIG. 3.

Now see Comparative Examples on FIGS. 2, 2A, 2B and 2C. In contrast tothe cited prior art, note that no ejector tabs are employed on theApplicants' lens perimeter itself (see FIG. 3), and most specifically,not at any location that would require cutting off before diphardcoating.

The Comparative Example of FIG. 2 shows a simplified 2-cavity lensmolding with cold sprue and runner (32). Note that each lens has amultiplicity of ejector tabs and the gate, each of which must be cut(33) in a separate operation afer demolding before dipcoating, usingmolded-on "T" shaped hanger tab (34). The prior art patent which mostclosesly resembles this Comparative Example of FIG. 2 is Weber (U.S.Pat. No. 4,008,031), differing only in that Weber's T shaped hanger tab20 is located directly opposite the gate 25, with an ejector tab 16 oneach side of tab 20. Weber needs to cut off the gate feeding into driptab 23 before dipcoating can be done.

Bakalar (U.S. Pat. No. 4,644,854), assignment to Neolens, shows in hisFIG. 4 & 5 use of ejector pin 15 opposite the gate, with no molded-onhanger tab shown. In actual practice, the Neolens molded lens has aplurality of ejector tabs and ejector pins which need to be cut beforedipcoating, in an array just like the Comparative Example of FIG. 2,thus needing 6 cuts (33) to prepare each lens for dipcoating using a tab(34) of unknown shape at the location pictured in FIG. 3.

Weymouth (U.S. Pat. No. 4,933.119), assignment to Gentex, shows noejector pins or hanger tabs, and does not teach any procedures fordemolding or ejecting the molded lens. One must only assume that a humanoperator is employed to manually remove the molded lens, in which casehigh levels of airborne contamination onto the demolded lenses isinherent. All Gentex Rx lenses show at least 1 cut per lens beforedipcoating (the cut is coated over with glossy film).

See now the Comparative Example of FIG. 2A, which shows a simplified4-cavity lens molding with cold sprue 18' and runner 35 feeding into 2pairs each of lenses, each having a gate 15'. Even if the closest priorart (Applicants' U.S. Pat. No. 4,878,969 and U.S. Pat. No. 4,900,242)were to be configured into 2 pairs as shown instead of 4 single lens,and even if a molded-on feature for gripping and fixturing were addedonto the runner for each pairs, there is still no way to dipcoat theselenses as they are demolded, without at least 2 cuts (33) to separatethe 4-cavity shot into the 2 pairs.

There are additional limitations Applicants' U.S. Pat. No. 4,878,969 andU.S. Pat. No. 4,900,242. See the ejection sequence in FIGS. 6, 7, and 8,wherein the resilient member 13 is kept in its compressed or, retractedposition, so that when ejector plate 17 is pushed forward by theinjection molding machine when the mold parting line is completely open,then the B-side inserts 5b is pushed forward past the parting lineplane, as shown in FIG. 8, and the molded optical lens or disk isejected 97, as shown. This method of Rx lens ejection is NOT desirablefor use with an in-line mold and dipcoat process scheme of the presentinvention, however. This reciprocating back-and-forth B side insert'smotion within a tightly-fitting bore of at least several millimeters(high-minus, finished-single-vision lenses can easily be 10 mm edgethickness) must inevitably cause metal-to-metal wear and resultinggalling (seen as scoring lines when viewing the molded lens edge; thisis confirmed by visual examination of the molded lens edge ofApplicants' licensee which uses this "traveling insert" method ofejection). The metal-to-metal wear that results must generate tiny metalparticulate contamination which can be deposited on both the moldedlenses and the part-forming surfaces of this optical mold, thus creatingcosmetic rejects in the (dipcoated lenses. Secondly, if severe gallingtakes place, the resulting irregular surface profile of the bore whichforms the mold cavity sidewall then permits molten plastic to flow intothese tiny galled-in crevices, which then gets sheared off duringejection forces (as the traveling insert is pushed forward), thuscreating a fine particulate plastic "dust" for further airbornecontamination of the demolded lenses and molding surfaces. For thesereasons, the traveling-insert method is found not to be acceptable forthe in-line, automated molding and dipcoating of the present invention.

Referring again to Applicants' U.S. Pat. No. 4,878,969 and U.S. Pat. No.4,900,242, note that FIG. 9B shows drip tabs 99 in the 6:00 o'clockposition of the molded lenses, but that even if there was a way ofseparating the two molded pairs shown without cutting aftersolidification of the plastic, the small cold well 31 is not locatedhigh enough to clear the lens edge so s to serve as a gripper or hangertab for dipcoating, nor can cold-runner firm sprue 19 be separatedwithout a cutting operation, which would generate plastic dustcontaminants.

Refer now to FIG. 2C Comparative Example, showing a typical prior artsingle lens with tab (34) at 12:00 o'clock position. If dipcoatingimmersion strokelength is not extremely accurate, and the lens isimmersed not just to the top lens edge but further partway up the stemof the tab, then the liquid will run back down by gravity this stem,thus causing flow runs (38) streaming back into the lens' optical faces.This is minimized but not entirely eliminated by reducing the tabthickness and setting tab (34) back some distance from either face.Weber (U.S. Pat. No. 4,008,031) is one such example.

Refer now to FIG. 2D Comparative Example, showing a Liebler (GB 2 159441A) prior art single lens with a tab (34) of the full thickness of thelens, at 12:00 o'clock position. Refer also to Liebler's FIG. 2, fromwhich this lens is taken, showing lens F with lug 10 and driptab 11. Ifdipcoating immersion stokelength is not extremely accurate (which isimpossible with Liebler's "endless conveyor" dipping the lens), the lenswill inevitably be immersed partway up the stem of the tab, then theliquid will run back down by gravity this stem thus causing a large flowruns (38) streaming back onto the lens' optical faces.

C. Lens Edge Detail Design for Clean Ejection

Refer back to Applicants' FIG. 1, which shows a drafted surface (19) ofthe mold cavity bore which forms the lens edge sidewall detail. In anoptional but preferred embodiment of the present invention, thissurface's draft angle will be a positive value, when compared tovertical ("zero draft"). This draft angle generally should be increasedin value directly proportionally as lens edge thickness is increased.Also, note that adding a slight molded-on rim at the junction of theconvex surface and lens edge sidewall (typically, no more than 0.5 mmper side is sufficient) which acts as a edge seal (42) (see FIG. 1B)facilitates compressed-air blowoff which is optional but preferred withthe present invention.

Molded or cast Rx lens blanks are sold in nominal diameters, rounded offto integral millimeters. Since all cast or molded plastic spectacle lensblanks are subsequently cut down on their perimeters so as to fit insidea specific spectacle frame of the patient's or prescribing doctor'schoice, inherently all Rx lenses will be "laid out" to fit the matingspectacle frame. Because of various blemishes and flaws which canaccumulate at the edge of cast Rx lens (such as bubbles or voids) andmolded plastic lens (such as residual knit line or gate blush) or, dueto the dip hardcoating (such as "dripmark"), the rule of thumb is toprovide a waste zone, consisting of a perimeter band of 5 mm widecircumferentially around the lens edge. Thus, on a 76mm-nomninal-diameter lens blank, for layout purposes, only the inner 66mm would be considered usable, when subtracting 5 mm waste zone perside.

The present invention utilizes the fact that waste zone exists in orderto alter lens product edge and sidewall details for improvedmanufacturability. Refer again to FIGS. 1. 1A and 1B. Most specifically,in an optional but preferred embodiment of the present invention,Applicants provide for a plurality of interchangeable sleeves (20), eachof which which can be selected with its different drafted surfaces (19)and assembled together with the appropriate mating convex insert (14) inorder to mold each different lens power, so as to provide the cleanestpossible release of the molded paired lenses free of solid metal orplastic particulates being generated by the ejection process. No onesuch sleeve draft angle or surface geometry can be optimum for all RxFSV lens molding, which must encompass a wide range of productgeometries. If too steep a draft angle is used all the way down the boreand sleeve surface which forms the lens sidewall, there will be a largeenough clearance gap formed between the sleeve and the insert to"flash", which is unacceptable. Specifically, to mold a complete matrixof FSV plus- and minus-powered lenses will require the mold design toaccomodate widely differing lens edge thickness. Plus-powered magnifyinglenses (for correcting farsightedness) will have typically, a minimallens edge thickness (2.0-0.8 mm). Conversely, demagnifying minus-poweredlenses (for correction of myopia and nearsightedness), will havecomparatively much thicker lens edge thicknesses (2.0-12.0 mm). Havingzero draft angle on the thickest lens edges would become problematical.Nevertheless, because the mold tooling becomes much more complicated,the prior art patents show no such provision for changeable oradjustable draft angles. In actual practice, measuring some commerciallyavailable Rx lenses believed to be made by the cited prior-art patentsshows a zero draft angle and, therefore, reliance upon "brute force" tomechanically push out the lens in spite of high retention forcestherein. Doing this also increases the probability of generating bothmetal-to-metal wear and shearing of metal to plastic, both of whichproduce solid particulate surface contaminations.

As shown in FIG. 1A and 1B, the present invention employsinterchangeable mold sleeves (20) which become the part-forming surfacesfor the lens' sidewall edge. By interchanging one set of such sleeveshaving a certain pre-determined drafted surface (19) with another sethaving a different pre-determined drafted surface/angle so as to matewith the corresponding B-side inserts for a specific desired FSV-powerminus lens, one can controllably increase or decrease the draft angle ofthe resulting molded paired lenses for the full range of FSV lenses asthey are ejected, for cleanest molded-lens quality. The thicker the lensedge, and correspondingly higher minus power, the greater the draftangle that should be applied, but preferably only part way down thesleeve. For example, a -2.00 Diopter lens may have an edge thickness of4.2 mm, and it will release cleanly with a drafted edge of only 1.9 mm.Conversely, a -5.00 Diopter FSV lens having a nominal edge thickness of14.6 mm has clean release by using an increased drafted edge of 7.2 mm.

D. Molded-On Tab Designs Suited For Robotic Manipulation in DipcoatingProcess Steps

After paired lens, having the above-mentioned elements of the presentinvention, are formed within multicavity injection-compression molds ofthe present invention and are solidified therein, demolding is donewithin a cleanroom enclosure maintained preferrably at a positivepressure (vs. ambient) from HEPA blower units. A take-out robot isneeded; preferably, the side-entry type, not "up and out" type, so thatmodular blowers supplying HEPA-filtered air can be located directlyabove the platens onto the molding machine, to maintain a preferrablypositive-air-pressure within the clean room enclosure whichsubstantially surrounds the mold (a deliberate gap located under themold for an air exhaust may improve the downward-directed laminar flowpattern; similarly a bottom gap for directed air exhaust is preferablylocated below the dipcoating machinery).

This side-entry takeout robot operates within a clean-room-enclosedtunnel between the enclosed mold and an enclosed HEPA-filtered automateddipcoating machine. When the mold is opened at the parting line and theside-entry takeout robot's arm is moved into position, each pair of lensare ejected forward into gripping jaws of end-of-arm tooling mounted onthe side-entry takeout robot's arm. In an optional but preferredembodiment, this robotic dipcoating machine with its self-contained,clean-room-filtered air, positive-pressure HEPA filter will be locatedbetween two such injection molding machines and multi-cavity molds, withtwo such side-entry robots feeding paired lenses into this one roboticdipcoating machine. This "duo line", in-line system may be economicallypreferred embodiment versus a single molding machine and mold fed to asingle coating machine, since typically Rx lens molding cycles arerelatively long (1-5 minutes, depending upon Rx lens power andcorresponding molding thickness). With longer-cycling lenses, the duoline configuration de-bottlenecks the molding step, for increasedcapacity output per unit of capital equipment cost.

See FIG. 4B. showing a block diagram flowsheet of the presentinvention's steps, within a single cleanroom enclosure (designated bythe dashed-line, showing all steps are performed within its cleanroomairspace perimeter).

This robotic device or dipcoating machine may take a number ofconventional forms with automated transport driven by chain-driveconveyors (operating singly or in parallel, connected by crossbarswhereon the lensholder racks would be hung), or, alternatively, anindexable overhead conveyor or walking-beam conveyor. An optional butpreferred embodiment employs a programmable SCARA cylindrical-type robotof the kind manufactured by IBM, GMF Fanuc, and Seiko. Such a SCARArobot should have a suitably-large (typically, up to 270 degreesrotation and at least 100 Z axis) work envelope, so as to be able totransfer these molded paired Rx lenses from a hand-off point somewhereinside the coating-machine clean-room enclosure to at least onehardcoating diptank, wherein a computer-programmable sequence ofimmersion times and withdrawal speeds can be employed, followed bytransfer to a holding device which is part of a curing workstationfitted with conveying means therein.

See FIG. 3, showing the paired molded lenses with hanger tab (1)comprising stem (3) and head (4), as they are received from theside-entry takeout robot directly or indirectly handed off to the secondrobotic device. Note dashed line (39) showing the liquid level of thedipbath--everything below that line (39) will be immersed in thehardcoating solution. Note the workholder-eating horseshoe-shaped head'scontoured surfaces (50 lead angle taper), (52 detent), and (53 insertionlead angle) are preferrably located above the liquid level (39). so asto not contaminate downstream area where mechanical mating mightdislodge coating flakes.

See now FIG. 3D. Preferably, this receiving second robotic device willbe a programmable SCARA cylindrical-type robot arm fitted with a rotarywrist (not shown) capable of rotationally moving (70) about axis (69),and paired gripping jaws ((43) left and (60) right) which can movetogether (68) to grip or ungrip, in accordance with the program. See nowFIG. 3C. Although the jaws are cut as substantially mirror-images of thehead surface contour s (50 lead angle taper),(52 detent), and (53insertion lead angle), there is additional clearances ((63) vertical and(62) horizontal) provided for imprecise robotic "handoffs" whentransferring the paired molded lenses from one workstation or operationstep to another. Such clearances provide tolerance for slightmisalignments or positional errors, yet complete the pickup or handoffproperly.

The gripping orientation shown in FIG. 3C is how the SCARA robot wouldhold the paired molded lenses during the dipcoating step's lowering andraising operations, after which the wet lenses can then be placed intoone of the multiple workholder arms having a substantially-matedmirror-image-machined "nest" of FIG. 3B having tapered angle (50'), andstem placement relief (57) and stem retention step (58), with stemclearance (56). Such a workholder will be then used to automaticallytransport the wet lens through drying and curing steps. Means for suchautomatically transport can be conventional conveyors, but in anoptional but preferred embodiment, a rotary index drive is fitted withmany such workholder arms, as a carousel within the curing workstation.

The gripping orientation shown in FIG. 3D is how the SCARA robot wouldhold the paired molded lenses during the insertion of the head into alensholder rack or similar fixture, wherein the receiving nest (notshown) has a protruding surface for mechanical interference with headdetent surface (52) to prevent the head from being easily dislodgedduring transport. Insertion then requires the robot to exert a pushingforce in the axial direction of the stem toward the head, sufficient todeflect the spring--the lead angle surfaces (53) assist in this frictionfit, as does the spring relief (51) (the greater the relief and thethinner the legs, the easier to deflect the horseshoe shaped spring).Removal is the reverse of the insertion. Typically, this insertion willbe done after the paired dipcoated lenses have been cured (at least to atackfree state), then inserted into a rack holding many pairs, fortransport manually after leaving the cleanroom to such other downstream"batch" operations as inspections (by humans), degating and packaging.

Another optional but preferred, embodiment uses an intermediate step ofrobotically placing the molded paired Rx lens into a circulatingfiltered alcohol tank for a prescribed residence time therein to performthe following functions:

1. De-statisizing (measuring surface charge by field meter, beforeimmersion, the lens has at least 4-10 electron volts' static charge,even after being held under ionizing blower for a prescribed period oftime; after alcohol-bath immersion of at least a couple of minutes, thelens has virtually no measurable surface charge).

2. Thermal cooling-off (measured immediately after demolding with anoncontact infrared pyrometer, the polycarbonate Rx lens typically showsa temperature of as high as 250° F. (125° C.) or higher; depending onresidence time and alcohol bath temperature, this can be reduced to120°-60° F., as may be required, depending upon solvent composition inthe liquid hardcoating bath, to prevent "solvent burn" of the moldedpolycarbonate lens surfaces. It is well-known to those skilled in theart that certain solvents found in today's state of art hardcoating bathcompositions can excessively attack a warm polycarbonate lens, causingcosmetic rejectable flaws due to excessive etching, frosting, andsolvent-burn phenomenon, while being tolerant of the same lens at lowertemperature.

3. Low-kinetic-energy cleaning/rinsing (soluble organic surface residuesand lightly-held insoluble particulates can be removed by thecirculating alcohol)

Advantages for using such an alcohol bath are evident especially if thehardcoating is solvent-based, since such solvents will typically attacka freshly-demolded hot (measured by noncontact infrared, actual temp canbe 250° F. (125° C.) or higher) polycarbonate lens surface to create anetch or partly-dissolved surface layer--both damaged surfaces areoptically rejected flaws. At room temperatures, the same dipbathsolvents may not harm the lens. The problem then is that cooling in airtakes many minutes, during which time even the best destaticizedpolycarbonate lens still has high enough surface charge (typically >3KV) to attract any airborne dusts which are further stirred up by thelocalized thermal air currents created by the hot lenses, so even in aHEPA cleanroom, the hot clean lenses gradually become cool less-cleanlenses. By immersing the hot paired lenses as soon as possible into thealcohol bath, they stay pristinely clean while heat is removed muchfaster (reducing the number of pairs of lenses held in the cooling stagebefore dipcoating, so the equipment can become more compact). andsurface charge becomes zero. For this immersion time of several minutesduration, it is best to have the robot place the paired lenses into analcohol tank fitted with a stainless steel cover (or inert plasticequivalent) into which has been machined as many multiple head-mating"nests" (as shown in FIG. 3B) as are needed--the longer the immersiontime desired, the more the number of nests and the larger the tank mustbecome.

If such an alcohol bath is utilized before dipcoating, it is possible towait too long--long enough after removal from the alcohol bath to letthe molded, paired lens dry completely before immersing it in the liquidhardcoating dipbath. To do so permits airborne particles to deposit ontothe cleaned dry lens surfaces, even briefly before entering into theliquid dipbath. Therefore, an optional, but preferred, embodiment foruse of the alcohol bath would not allow complete evaporation of thealcohol wet film off the molded paired Rx lens before immersion into theliquid hardcoating dipbath. Instead, wet alcohol films should remain onthe lens when immersed into the dipbath, where the lenses are kept for asufficiently-long residence time so as to remove any remaining wet-filmof alcohol (and any airborne particles which may have become entrainedtherein during the transfer time from alcohol bath to dipcoating bath).Displacing wet-films of alcohol on the lenses' surface with the liquidhardcoating bath is achieved by a combination of high rate of internalcirculation of the liquid hardcoating, as well as some programmed-inmechanical motion by the robotic arm holding the lenses to provideagitation and turbulence.

This SCARA-dipping and alcohol-bath approach assumes that the liquidhardcoating bath composition contains at least one or more alcohols insome significant percentage, and that gradual increase during operationswithin a certain % range of alcohol by dragout of the wet film onto themolded lens will not disrupt desired solvent balance and drydowncharacteristics of the liquid hardcoating dipbath. Such liquidsolvent-based hardcoating compositions ideally suited for this protocoland for use with the SCARA robot will also be of low-to-moderateviscosity (preferrably, <10 centistoke; most preferably, <5 cs.), so asto give efficient mixing/removal of the wet alcohol film off the lenswithin the dipbath without entraining air bubbles, and to easily flowout smoothly after any vibrations from the SCARA dipping motions.Another way to get smooth coatings from such unconventionally thinviscosity (2-10 cs.) dipbaths is to employ unconventionally fastwithdrawal speeds (at least 20 inches per minute, preferrably 0.5-5inches per second, most preferrably 1-3 inches per second; conventionaldipbaths of >10 cs. use 2-12 inches per minute), and to follow the firstdip with at least a second dip. In such a preferred fast withdrawalspeed double-dip process, the dipbath should be relatively fast-drying(by choosing selected high-evaporation-rate solvents such as lowmolecular weight alcohols and ketones), so as to give smooth coatingsfree of coating flow runs or "sags", while using relatively dilute(typically <25% solids) dipbath with a moderate-to-low hardcoatingpolymer molecular weight. Depending upon the chosen liquid hardcoatingcrosslinking chemistry, the curing workstation will be configured so asto provide the desired cure protocol. For example, a simplest versionwould be a solvent-free UV-curable hardcoating in which case the curingworkstation might simply consist of a battery of UV lamps of theelectrodeless type (made by Fusion Systems of Rockville, Maryland) orconventional mercury-are UV lamps, with the lenses having beenrobotically placed onto carriers of suspended from an overhead conveyor,so as to present the paired, molded lenses' front and back surfaces toline-of-sight exposure to these UV lamps for a sufficiently-long time toeffect desired cure. However, doing so may preclude use of the alcoholbath. Another variant of such a configuration would be solvent-based UVcure, in which case a solvent drydown stage would precede theUN-cure-lamp stage (infrared lamps represent an energy-efficient way ofdevolatilizing such coatings, provided again that the molded. paired Rxlens are presented in line-of-sight orientation to this bank of infraredlamps), to dry both front and back lens surfaces. Then the principles ofthe above paragraph may apply.

All commercially-desirable heat-curing liquid hardcoats aresolvent-based, so inherently a solvent-evaporation/coating-drydown stagemust be employed before accelerated heat cure is given. As previouslymentioned, if the lens orientation permits line-of-sight exposure to abank of infrared lamps, doing so is an energy-efficient way of achievingthis end. Once fully devolatilized, additional exposure to infrared canprovide full croslinking, or, optionally, a lesser dosage can providegelation to a sufficiently hard film so as to be "tackfree" (meaningairborne dusts will not permanently stick to such surfaces, so tackfree,hardcoated lenses can safely be handled manually outside the clean-roomenclosure without resulting in yield loss due to coating clear specks.Optionally, a tackfree state might be desired in order to re-cycleflawed coated lenses--any inspected lenses which have coating flaws (anbe easily recycled by immersion into a suitable solvent to strip thetackfree gelled coating which is not yet fully crosslinked, thusremoving the flawed coating film and allowing the paired molded lensesto again be fed through the cleaning and dipcoating protocol.

An optional but preferred embodiment of a curing workstation may employa rotary indexing table fitted with multiple arms, having eithergrasping jaws, suction cups or sculptured mechanical nests, adapted forreceiving the molded paired Rx lenses that have molded-on hanger tabs.An especially preferred embodiment employs the SCARA robot to preciselyplace the head of the hanger tab into a substantially mechanicallymating geometry (preferably with a tapered lead-angle fit) nest of thetype shown in FIG. 3B, and located near the end of each of these arms.

A further optional but preferred embodiment of this special type ofcuring workstation would then allow for a settable rotation of the arm,such that the position of the molded, paired Rx lens can be varied froma "straight down" vertical orientation (wherein the molded, pairedlenses hanging vertically direct down from the arm, at a 90-degreeangle), and by rotation of the arm this angle can be successivelyreduced to some minimal angle of perhaps 10 degrees or so below thehorizontal orientation. (See FIG. 3B, retention step (58)) Thisoptional, but preferred, embodiment has the advantage of employinggravity to create a more uniform coating flowout pattern distributed allacross the lens surface. This is believed to be especially important forthose Rx lenses having strong plus powers (steep, convex front curvedsurfaces), and also multi-focal lenses having a ledged bifocal ortrifocal segment ("D seg"). Those two types of lenses are particularlyproblematical when the coating is dried and cured in a substantiallyvertical orientation due to gravity then increasing the nonumiformity offlowout of the liquid hardcoating. Refer to Weber (U.S. Pat. No.4,443,159) coating patent.

E. Process Flowsheets for Add-On Steps in Continuous-Process, following"Mold and Dipcoat"

In yet another optional but preferred embodiment, after the molded andhardcoated lenses are cured at least to a tackfree state, the lenses arethen robotically transferred into an adjoining extension of the samecleanroom enclosure which contains an automated computer-assisted-visionlens inspection system, for cosmetic inspection. See FIG. 4C. Suchautomated lens inspection machines typically use pattern recognitioncomputer software with a video and/or laser-scanning noncontactinspection, and make comparison of the resulting image against thecomputer's decision rules for "go" and "no-go" acceptance of anycosmetic flaw deviations. However, such an optical computerizedinspection system for cosmetics relies upon high-resolution imagery anda large proportion of all cosmetic rejects are at the surface of thehardcoated lenses ("coating clear specks" and "coating flowout runs",especially). One such manufacturer of Rx FSV lens automated inspectionmachines is Non-Contact International, of Maumee, Ohio.

Such inspection system in giving desired results (i.e., rejecting badlenses and accepting good lenses) must not reject "good" lenses whichonly have a lightly-held dust particle laying loosely on the lenssurface. Cleanliness of the lenses coming into the inspection system isthe biggest problem in its use so far. Elaborate and costly multi-stagecleaning equipment workstations and protocols have been necessitated toproperly use such equipment. A particularly advantegeous combination ofthe present invention with such machines would employ this matedcleanroom (so the lens never leaves the Class 100 clean air environment)operating with positive pressure without any human operator within thatairspace, so that paired tackfree-hardcoated lens are kept in a pristinestate as they leave the curing workstation directly to the videoinspection station. Cosmetic rejects caught at this tackfree state canthen be robotically set aside and recycled through solvent stripping,re-cleaning, and re-dipcoating, as mentioned earlier.

See flowsheet of FIG. 4D. Yet another optional but preferred embodimentof the present invention takes the hardcoated lens to full crosslinkedstate before leaving the curing workstation, then robotically transfersthe molded fully-cured hardcoated paired Rx lens within an adjoiningextension of this mated clean-room enclosure maintained under positivepressure (HEPA-filtered air of typically Class 100 purity). wherein thisconnected-clean-room enclosure contains a thin-film anti-reflective("AR") vacuum-coating machine fitted with multiple load locks andproduct workholders adapted to the molded, hardcoated, paired lenses.FIG. 4D shows a block diagram flowsheet of the present invention'ssteps, within a single cleanroom enclosure (designated by thedashed-line, showing all steps are performed within its cleanroomairspace perimeter). This continuous-process anti-reflective vacuumcoating system would typically contain the following steps:

1. After the load station, pull at least a rough vacuum beforetransferring to a second vacuum stage via load lock, wherein a finalvacuum is pulled.

2. At that point, some surface preparation protocol, such as ionizingplasma or electron gun discharge, can be used to clean and/or modifysurface chemistry of the top few molecular layers of the hardcoated Rxlens, either in this chamber or in the next chamber connected by loadlock.

3. Once such surface preparation is completed, robotic transfer via loadlock moves the paired lens into the vacuum-deposition) chamber, whereinan AR film is deposited. Preferably, a high-arrival-energy type AR filmis deposited by sputttering or by ion-gun-assist, so as to provide adesirably-dense and strongly-adherent coating AR film onto one or bothoptical surfaces of the hardcoated paired lens.

Such a continuous-process automated-transfer AR-coating machine would bedirectly analogous to similar machines used by the hundreds forcontinuous-process aluminum-sputter-coating onto injection-moldedpolycarbonate compact discs. Leading vacuum-coating equipmentmanufacturers as Leybold, Balzers, and Denton Vacuum have provided suchmachines for integrated-molding-and-coating of compact discs (CDs).

We claim:
 1. An injection-compression molding process for reducedparting line flash on at least one molded thermoplastic article, withina moldset mounted within an injection molding machine havingprogrammable control of means for applying clamping forces and openingforces onto a parting line formed between an A side and an B side ofsaid moldset, and the injection molding machine having programmablecontrol of means for moving forward or back an ejector assembly withinthe B side of said moldset using said moldset having at least oneedge-gated variable-volume mold cavity, said mold cavity havingpartforming surfaces on opposing paired A side insert and B side insertfacing the parting line, wherein at least one extendable andcompressible passive resilient member of varying length which determinesa cavity height dimension of said mold cavity within preset mechanicallimits, the resilient member being an operative combination ofi) steelcoil die spring to provide a moderate spring force over a long distancein a first clamping position of said moldset, with ii) stackedBelleville steel spring washers to provide a stiff spring force over ashort distance in a second clamping position of said moldset, theresilient member being mounted between a side parting line mold plateand B side clamp plate of said moldset and exerting combined springforces to bias forward the B side parting line mold plate toward theparting line, such that when there is less clamping force exerted by theinjection molding machine than a first spring force equal to the steelcoil die spring force acting alone to bias forward the B side partingline mold plate toward the parting line, the resilient member lengthwill be a maximum within the preset mechanical limits in the firstclamping position of said moldset, and when there is more clamping forcethan the first spring force equal to the steel coil die spring forceacting alone to bias forward toward the parting line but less clampingforce than a second spring force equal to the steel coil die springacting together with steel spring washer force to bias forward the Bside parting line mold plate toward the parting line, the resilientmember length will be an intermediate value in a second clampingposition of said moldset, and when there is more clamping force than thesecond spring force equal to the steel coil die spring acting togetherwith steel spring washer force to bias forward the B side parting linemold plate toward the parting line, the resilient member length will bea minimum within the preset mechanical limits in a third clampingposition of said moldset, the process comprising the steps of:a.)Pre-enlarging said mold cavity by substantially closing a perimeter ofsaid mold cavity at the parting line so as to prevent moltenthermoplastic from flashing, in the first clamping position of saidmoldset, such that a first cavity height equal to the sum of the desiredcompression strokelength plus a final thickness of the molded article isdetermined, before injection starts b.) Partially filling said moldcavity after injection has started by progressively reducing cavityheight to the second clamping position, by increasing clamp forceapplied to exceed the first spring force but less than the second springforce; c.) Completely filling said mold cavity by further progressivelyreducing cavity height to reach the third clamping position of saidmoldset, by increasing clamp force applied to exceed the second springforce; d.) Cooling said molded article within said mold cavity until thethermoplastic is shape stable, by maintaining cavity heightsubstantially at the third clamping position of said moldset; e.)Ejecting said molded article by releasing clamp force and opening themoldset along the parting line.
 2. An injection-compression moldingprocess of claim 1 wherein said edge gated variable volume mold cavityis in fluid communication with a nozzle of the injection molding machineso as to form at least a cold sprue and gate having a B side mechanicalretention, and said molded article has a perimeter edge having a draftedsurface suited for clean release from a bore of said mold cavity, andejecting said molded article by releasing clamp force and opening themoldset along the parting line comprises the steps of:e.) extending theresilient member while decreasing clamp force applied to less than thefirst spring force, thereby separating said molded article from thepartforming surface of B side insert and creating a release space,before the parting line formed between A side and B side separates f.)pulling said molded article off the partforming surface of the A sideinsert as the parting line begins to separate, while mechanicallyretaining said molded article onto the B side; g.) stripping said moldedarticle off the B side mechanical retention, once the moldset is fullyopen along the parting line.
 3. An injection-compression molding processof claim 1 wherein stripping said molded article off the B sidemechanical retention, once the moldset is fully open along the partingline but only after an end-of-arm tooling of a takeout robot is in placeto receive said molded article.